Right now Digit can only save from and withdraw funds to one personal checking account (no business or savings accounts just yet!). Support for multiple checking accounts and different types of bank accounts is a request we see frequently, and something we'll be looking to implement down the road.
To keep things safe, Digit is a closed-loop system, meaning funds withdrawn from your Digit savings account can only be returned to the same checking account they were debited from (or sent to you via check if that account has since been closed).
For now, we recommend connecting to your most active account (i.e. where you get paid, do most of your spending from).